diff options
author | Peter Zijlstra <peterz@infradead.org> | 2021-04-20 10:18:17 +0200 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-09-12 08:56:39 +0200 |
commit | 56c77c1b522928d86738e0d22d1adba44dc9c64b (patch) | |
tree | 07e9b10c87b75365c1f963d4740c1da1b4c49b97 /kernel | |
parent | af3cf928b9989877487f7ec6b34e9f31d9d89a09 (diff) |
kthread: Fix PF_KTHREAD vs to_kthread() race
commit 3a7956e25e1d7b3c148569e78895e1f3178122a9 upstream.
The kthread_is_per_cpu() construct relies on only being called on
PF_KTHREAD tasks (per the WARN in to_kthread). This gives rise to the
following usage pattern:
if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p))
However, as reported by syzcaller, this is broken. The scenario is:
CPU0 CPU1 (running p)
(p->flags & PF_KTHREAD) // true
begin_new_exec()
me->flags &= ~(PF_KTHREAD|...);
kthread_is_per_cpu(p)
to_kthread(p)
WARN(!(p->flags & PF_KTHREAD) <-- *SPLAT*
Introduce __to_kthread() that omits the WARN and is sure to check both
values.
Use this to remove the problematic pattern for kthread_is_per_cpu()
and fix a number of other kthread_*() functions that have similar
issues but are currently not used in ways that would expose the
problem.
Notably kthread_func() is only ever called on 'current', while
kthread_probe_data() is only used for PF_WQ_WORKER, which implies the
task is from kthread_create*().
Fixes: ac687e6e8c26 ("kthread: Extract KTHREAD_IS_PER_CPU")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Link: https://lkml.kernel.org/r/YH6WJc825C4P0FCK@hirez.programming.kicks-ass.net
Signed-off-by: Patrick Schaaf <bof@bof.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/kthread.c | 43 | ||||
-rw-r--r-- | kernel/sched/fair.c | 2 |
2 files changed, 30 insertions, 15 deletions
diff --git a/kernel/kthread.c b/kernel/kthread.c index b2bac5d929d2..63f7eb3c2640 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -76,6 +76,25 @@ static inline struct kthread *to_kthread(struct task_struct *k) return (__force void *)k->set_child_tid; } +/* + * Variant of to_kthread() that doesn't assume @p is a kthread. + * + * Per construction; when: + * + * (p->flags & PF_KTHREAD) && p->set_child_tid + * + * the task is both a kthread and struct kthread is persistent. However + * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and + * begin_new_exec()). + */ +static inline struct kthread *__to_kthread(struct task_struct *p) +{ + void *kthread = (__force void *)p->set_child_tid; + if (kthread && !(p->flags & PF_KTHREAD)) + kthread = NULL; + return kthread; +} + void free_kthread_struct(struct task_struct *k) { struct kthread *kthread; @@ -176,10 +195,11 @@ void *kthread_data(struct task_struct *task) */ void *kthread_probe_data(struct task_struct *task) { - struct kthread *kthread = to_kthread(task); + struct kthread *kthread = __to_kthread(task); void *data = NULL; - probe_kernel_read(&data, &kthread->data, sizeof(data)); + if (kthread) + probe_kernel_read(&data, &kthread->data, sizeof(data)); return data; } @@ -490,9 +510,9 @@ void kthread_set_per_cpu(struct task_struct *k, int cpu) set_bit(KTHREAD_IS_PER_CPU, &kthread->flags); } -bool kthread_is_per_cpu(struct task_struct *k) +bool kthread_is_per_cpu(struct task_struct *p) { - struct kthread *kthread = to_kthread(k); + struct kthread *kthread = __to_kthread(p); if (!kthread) return false; @@ -1272,11 +1292,9 @@ EXPORT_SYMBOL(kthread_destroy_worker); */ void kthread_associate_blkcg(struct cgroup_subsys_state *css) { - struct kthread *kthread; + struct kthread *kthread = __to_kthread(current); + - if (!(current->flags & PF_KTHREAD)) - return; - kthread = to_kthread(current); if (!kthread) return; @@ -1298,13 +1316,10 @@ EXPORT_SYMBOL(kthread_associate_blkcg); */ struct cgroup_subsys_state *kthread_blkcg(void) { - struct kthread *kthread; + struct kthread *kthread = __to_kthread(current); - if (current->flags & PF_KTHREAD) { - kthread = to_kthread(current); - if (kthread) - return kthread->blkcg_css; - } + if (kthread) + return kthread->blkcg_css; return NULL; } EXPORT_SYMBOL(kthread_blkcg); diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 74cb20f32f72..87d9fad9d01d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7301,7 +7301,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) return 0; /* Disregard pcpu kthreads; they are where they need to be. */ - if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p)) + if (kthread_is_per_cpu(p)) return 0; if (!cpumask_test_cpu(env->dst_cpu, p->cpus_ptr)) { |